1. Field of the Invention
The present invention relates to a semiconductor device having a trench MOS (Metal Oxide Semiconductor) gate structure and a method for fabricating the same.
2. Description of Related Art
A trench MOS gate structure, in which a trench (groove) is formed in a semiconductor substrate and a gate oxide film and a gate electrode are formed in the trench, has been employed in semiconductor devices such as a power MOSFET (Field Effect Transistor) or the like and is widely used for a DC-DC converter, load switch, or the like of electronics equipment. With the recent trend of low power consumption and high speed of electronic equipment, demand for decrease in on-resistance of a MOSFET used in the equipment is growing.
An example of a MOSFET which has a trench MOS gate structure designed for reducing on-resistance is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2005-45123. FIG. 9A is a plan view of a conventional semiconductor device. FIG. 9B and FIG. 9C are cross sections taken along the line IXb-IXb and the line IXc-IXc, respectively, of the semiconductor device of FIG. 9A.
As shown in FIG. 9A through FIG. 9C, a conventional semiconductor device includes: a low concentration p-type body region 103 formed on an n-type drain region 102a; an n-type source region 104 and a high concentration p-type body region 105, both formed on the low concentration p-type body region 103; a plurality of trenches T arranged in stripes and each being formed from top faces of the n-type source region 104 and the high concentration p-type body region 105 and passing through the n-type source region 104, the high concentration p-type body region 105, and the low concentration p-type body region 103 to reach into the n-type drain region 102a; a gate insulating film 106 formed along an inner face of each trench T; a gate electrode 107 buried in each trench T; an insulating film 108 (not shown in FIG. 9A) formed on the gate electrode 107 in each trench T; a source electrode (not shown) formed on the n-type source region 104, high concentration p-type body region 105, and insulating film 108; and a drain electrode (not shown) formed under the n-type drain region 102a. The n-type drain region 102a is composed of a high concentration n-type drain region 101, which is made of a silicon substrate, and a low concentration n-type drain region 102.
As above, by arranging the trenches in stripes to reduce trench width and increasing the density of transistors per unit area by decreasing the distance between trenches located next to each other with the n-type source region 104 and the high concentration p-type body region 105 interposed therebetween to increase channel width, it is possible to reduce on-resistance.